U.S. patent number 6,749,681 [Application Number 10/070,931] was granted by the patent office on 2004-06-15 for method of producing cement clinker and electricity.
This patent grant is currently assigned to Alstom Technology LTD. Invention is credited to Vassilios Burdis, Shin G. Kang, Srivats Srinivasachar, Majed Toqan.
United States Patent |
6,749,681 |
Burdis , et al. |
June 15, 2004 |
Method of producing cement clinker and electricity
Abstract
In a method of producing cement clinker and electricity, cement
raw mix and hydrocarbon are fed in a circulating fluidized bed
boiler (1). Therein cement raw mix is calcined and steam is
produced. Gas and solids out of the fluidized bed enter a cyclone
(8), the solids being separated therein and returned to the bed.
Part of those solids are first cooled down in a solids heat
exchanger (9) producing steam. Fly ash consisting predominantly of
lime and gas escaping the cyclone are passed through a heat
exchanger (28, 33) and a filter (37). Hot bed material is
discharged from the circulating fluidized bed and is ground with
additives, then blended with lime being separated in the filter
(37), then supplied to a rotary kiln (16), wherein the solids are
clinkered. The produced steam is fed to a steam turbine island
(42).
Inventors: |
Burdis; Vassilios (Butzbach,
DE), Kang; Shin G. (Simsbury, CT), Srinivasachar;
Srivats (Sturbridge, MA), Toqan; Majed (La Celle St.
Cloud, FR) |
Assignee: |
Alstom Technology LTD (Baden,
SE)
|
Family
ID: |
8243025 |
Appl.
No.: |
10/070,931 |
Filed: |
June 26, 2002 |
PCT
Filed: |
September 13, 2000 |
PCT No.: |
PCT/CH00/00493 |
PCT
Pub. No.: |
WO01/19750 |
PCT
Pub. Date: |
March 22, 2001 |
Foreign Application Priority Data
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Sep 16, 1999 [EP] |
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99810828 |
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Current U.S.
Class: |
106/744; 106/739;
106/761 |
Current CPC
Class: |
C04B
7/36 (20130101); C04B 7/475 (20130101); C04B
7/43 (20130101); C04B 7/434 (20130101); F22B
31/0084 (20130101); Y02P 40/123 (20151101); Y02P
40/121 (20151101) |
Current International
Class: |
C04B
7/00 (20060101); C04B 7/36 (20060101); C04B
7/43 (20060101); C04B 7/47 (20060101); F22B
31/00 (20060101); C04B 007/36 () |
Field of
Search: |
;106/744,739,761 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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689 830 |
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Dec 1999 |
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CH |
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1092692 |
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Apr 2001 |
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EP |
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Other References
Database WPI. Section CH, Week 199231, Derwent Publications Ltd.,
London, GB, SU 1 675 254 A, publication Sep. 7, 1991, abstract
only..
|
Primary Examiner: Marcantoni; Paul
Attorney, Agent or Firm: Burns, Doane, Swecker & Mathis,
L.L.P.
Claims
What is claimed is:
1. In a method of producing cement clinker and electricity,
comprising feeding cement raw mix and hydrocarbon in a circulating
fluidized bed, calcining the cement raw mix in the circulating
fluidized bed and producing steam therein, discharging hot bed
material in a rotary kiln, clinkering the calcined material in the
rotary kiln and subsequently cooling the clinker, further
comprising the gas and the solids out of the fluidized bed entering
a cyclone, the solids being separated therein being returned to the
bed, whereby part of those solids being first cooled down in a
solids heat exchanger producing steam, whereas the gas and the fly
ash escaping the cyclone being passed through at least one heat
exchanger and through a filter, further comprising the produced
steam being fed to a steam turbine island comprising a steam
turbine being drivingly connected to a generator, the improvement
comprising feeding part of the cement raw mix in pulverized form,
lime-rich fly ash obtained from calcination of limestone from the
pulverized part of the cement raw mix escaping the cyclone system,
feeding the predominant part of the remaining part of the cement
raw mix in crushed form for forming bed and circulating material,
and grinding the hot bed material as well as additives before
blending them with lime being separated in the filter, separated in
the filter, obtained from calcination of limestone in the cement
raw mix.
2. A process according to claim 1, wherein the discharged hot bed
material is cooled before grinding.
3. A process according to claim 1, wherein the calcined pulverized
lime escaped from the cyclone and separated in the filter is
supplied to the clinkering process.
4. A process according to claim 1, wherein carbon contained in the
fly ash escaped from the cyclone and separated in the filter and
the carbon added via discharged hot bed material is supplied to the
clinkering process as a fuel.
5. A process according to claim 4, wherein the total amount of
combustible material needed for the clinkering process is
controlled in function of the carbon added via the filter and the
carbon added via the discharged hot bed material.
6. A process according to claim 4, wherein the amount of combustion
air needed for the clinkering process is controlled in function of
the additional carbon separated in the filter and the carbon added
via the discharged hot bed material.
7. A process according to claim 3, wherein part of the calcined
pulverized lime escaped from the cyclone and separated in the
filter is re-injected into a line upstream the filter to improve
sulfur removal efficiency by simultaneously controlling the
relative humidity in the flue gas.
8. A process according to claim 1, wherein the calcined raw mix is
preheated before entering the clinkering process.
9. A process according to claim 4, wherein the gas and the fly ash
escaping the cyclone and entering the steam producer are cooled at
a fast rate in order to avoid recarbonation of lime.
10. A process according to claim 1, wherein the exhaust gases from
the kiln and the cyclone are added to the gases exhausting the
circulating fluidized bed cyclone in order to match pressure
conditions.
11. A process according to claim 1, wherein the predominant portion
of the sensible heat in the clinker exiting the clinkering process
is used for generating steam.
12. A process according to claim 1, wherein part of the flue gas
discharged from clinkering process is passed through a scrubber,
wherein gypsum is produced.
13. A process according to claim 1, wherein the at least one heat
exchanger is utilized for preheating air being fed to the bed as
fluidizing air and overbed air.
14. A process according to claim 1, wherein the at least one heat
exchanger is a steam producer followed by an air heater.
15. A process according to claim 1, wherein the part of the cement
raw mix fed in pulverized form into the circulating fluidized bed
is the predominant part.
Description
FIELD OF THE INVENTION
The invention relates to a method of producing cement clinker and
electricity, comprising feeding cement raw mix and hydrocarbon in a
circulating fluidized bed, calcining the cement raw mix in the
circulating fluidized bed and producing steam therein, discharging
hot bed material in a rotary kiln, clinkering the calcined material
in the rotary kiln and subsequently cooling the clinker, further
comprising the gas and the solids out of the fluidized bed entering
a cyclone, the solids being separated therein being returned to the
bed, whereby part of those solids being first cooled down in a
solids heat exchanger producing steam, whereas the gas and the fly
ash escaping the cyclone being passed through at least one heat
exchanger and through a filter, further comprising the produced
steam being fed to a steam turbine island comprising a steam
turbine being drivingly connected to a generator.
DISCUSSION OF BACKGROUND
U.S. Pat. No. 4,425,163 describes a method for producing cement
clinker, in which raw cement powder is calcined to a level of at
least 95% in a circulating fluidized bed and then clinkered in a
rotary kiln. The circulation system comprises a fluidized bed
reactor, a cyclone separator and a recycling duct. The carbonaceous
fuel supplied to the calcining fluidized bed reactor is burnt near
stoichiometrically in two stages with fluidizing gas and secondary
gas. This method requires a preheating of the raw material in a
suspension type heat exchanger.
A method of producing cement clinker and electricity as described
above in the "field of the invention" is known from the article
"Challenges of circulating fluid bed reactors in energy and raw
material industries" by Lothar Reh, published in DECHEMA Deutsche
Gesellschaft fur chemisches Apparatewesen, Chemische Technik und
Biotechnologie e.V., Frankfurt am Main. This article is based on a
lecture held on the 6th International Conference on Circulating
Fluidized Beds, in Wurzburg, Germany on Aug. 22-27, 1999. This
article describes trigeneration of cement, electricity and heat
from high-ash coal using Circulating Fluidized Bed-Technology.
Limestone and high-ash coal are separately prepared and ground
before feeding them into the boiler. These two basic raw materials
are proportioned online. Sulfur is completely bound into the bed
material, which has the chemical composition of clinker. The hot
bed material is discharged directly into a small rotary kiln. This
direct use of ash substituting the clay component in cement avoids
disposal of ash completely. This known method requires high
performance cyclones in order to catch and recycle the pulverized
limestone and/or lime and the grinding of the high-ash coal prior
to its entry in the boiler.
SUMMARY OF THE INVENTION
Accordingly, the object of the invention is to provide a novel
method and plant for integrating a cement clinker-buming unit into
a hydrocarbon, especially coal-fired power plant, using circulating
fluidized bed technology.
This is achieved, according to the invention, by following means
feeding part of the cement raw mix in pulverized form, designing
the cyclone system so as the lime-rich fly ash obtained from
calcination of limestone from the pulverized part of the cement raw
mix escapes the cyclone system, feeding the predominant part of the
remaining part of the cement raw mix in crushed form for forming
bed and circulating material, and grinding the hot bed material as
well as additives before blending them with lime being separated in
the filter, obtained from calcination of limestone in the cement
raw mix.
The advantages of the invention are to be seen in a significantly
smaller number of cyclones leading to lower capital cost, because
the cyclone system may have a larger cut size than the above
mentioned prior art devices. It has a lower pressure drop, which
leads to lower power consumption and lower operation cost. It also
has a higher reliability due to the absence of fines in the
material collected in the cyclone, which becomes easier to
discharge. Another advantage is seen in the fact that there is no
need to grind the fuel feed. Lastly the nitric oxide emissions are
lower.
The discharged hot bed material may be cooled before grinding. This
allows reliable operation of the downstream grinding equipment and
gives an opportunity for further steam production.
The heat exchanger cooling the flue gas and the fly ash may be
completely utilized for preheating air that is fed to the bed as
fluidizing and overbed air. This requires only one piece of
equipment, resulting in a high temperature driving force for steam
generation in the remainder of the system. Another advantage is the
short residence time of the gases and the fly ash in the heat
exchanging apparatus, thus avoiding recarbonation of the lime to
CaCO.sub.3.
The at least one heat exchanger may also be a steam producer
followed by the air heater. In this case, it is preferable to cool
the gas and the fly ash escaping the cyclone and entering the steam
producer at a fast rate in order to avoid recarbonation.
BRIEF DESCRIPTION OF THE INVENTION
A more complete appreciation of the invention and many of the
attendant advantages thereof will be readily obtained as the same
becomes better understood by reference to the following detailed
description when considered in connection with the accompanying
drawing, which illustrates diagrammatically an exemplary embodiment
of the invention with coal as hydrocarbon. Only the elements
essential for understanding the invention are shown. Arrows
illustrate the flow direction of the working media.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawing, the equipment necessary for
performing the cement and electricity production consists mainly of
a circulating fluidized bed reactor 1, called hereafter CFB, a
cement plant and a steam turbine island 42.
The equipment necessary for performing the cement production
comprises mainly three blocks, namely the same CFB acting as a raw
mix preheater and calciner, a kiln 16 and a clinker cooler 20. The
basic idea is to have used the circulating fluidized bed combustor
as steam boiler and as calciner for the cement raw mix.
Regarding the preheating of the air needed for cooling the cement
clinker, for cinkering the cement raw mix, and for oxidizing the
hydrocarbon, which is coal in this embodiment.
Via air intake line 23, ambient air is sucked in the system by a
fan 22 to a clinker cooler 20 and heated therein by cooling down
the cement clinker. The heated air exits the clinker cooler via
line 44. This air is now divided into two streams. A first stream
is supplied to the kiln 1.6 via line 25 as kiln combustion air. The
second stream bypasses the kiln via line 26 and is fed into a riser
tube 51 for combustion of fuel to preheat the cement raw mix.
Via air intake line 29 the major portion of ambient air is sucked
by a fan 27 in the system. This air is preheated in an air
preheater 28, which might be of the Ljungstrom-type. Via line 30
the air is fed to the combustor 1, in which it penetrates via a
fluidizing air supply 5 and a secondary or overbed air supply
4.
Regarding the "Steam" Production
Depending on the apparatus type, the gas/air mixture can be
introduced into the combustor on different levels. In the example
shown on the drawing, in which the reactor is an upright
circulating fluidized-bed steam generator with a flow stream from
bottom to top, the fluidizing air is introduced at the bottom
through an air distributor. The secondary air is fed through one or
more elevations of ports in the lower combustor. The reactor is
provided with four other inlets. One carbonaceous residue supply
line 6, one inlet 2 for the coal and two inlets 3 and 3a for the
raw cement mix.
Coal (and sorbent) is introduced mechanically or pneumatically to
the lower portion of the reactor via supply 2. This coal can be
either crushed or pulverized. Like the air, coal may be injected on
different levels of the reactor. If the coal is in form of crushed
material with a size of approximately 6-mm, it can be fed by
gravity.
Combustion takes place throughout the combustor, which is filled by
bed material. Flue gas and entrained solids leave the combustor and
enter one or more cyclones 8, where the solids are separated.
The flue gas and the fly ash exit the gas outlet of the separation
device 8 via a flue gas line 32. These separated gases are further
treated before disposal. They are first cooled down in a gas cooler
33, thereby heating up water in an economizer 34 integrated in the
water/steam cycle of a steam turbine island 42. In order to avoid
recarbonation of the lime, the gases in line 32 are cooled at a
fast rate, i.e. greater than 30.degree. C./sec. Downstream the
gases are further cooled in the air preheater 28. The gas is
supposed to leave this gas cooler 28 with a temperature of about
100-150.degree. C. Downstream the gas cooler a solids filter 37 is
provided in the line 38 to remove from the gas all the remaining
solids. This filter 37 could be a fabric filter or an electrostatic
precipitator. A fan 40 is installed in the gas line exiting the
filter, preferably on the clean side of the filter 37. Its purpose
is to control the pressure in the system close to atmospheric
conditions. The cleaned gas leaves the system via the stack 41. The
solids separated in the filter 37 are a major feature of the
invention. They are fed via line 39 to an appropriate location in
the cement system.
The solids separated in the cyclone 8 are recycled to the combustor
via line 6. The major portion is directly returned to the
fluidizing bed via line 7. Some solid is diverted via line 10 to an
external fluidized-bed heat exchanger 9 and then added to the
portion in line 7. The bed temperature in the combustor 1 is
essentially uniform and is maintained at an optimum level for
sulfur capture and combustion efficiency by heat absorption in the
walls of the combustor. In the present example the heat exchange is
supposed to occur in an evaporator 35. Superheating of the steam
and--for large steam turbine units with a reheat cycle--reheating
is performed preferably by further heat removal from the hot solids
absorption in the fluidized-bed heat exchanger 9 and/or in the
gas-cooler 33. This heat exchanger 9 is containing immersed tube
bundles. The flow rate of the solids through apparatus 9 via line
10 can be used to control the steam temperature. The produced
superheated steam is fed to the turbine island 42 comprising at
least one steam turbine driving a generator producing electrical
power. Additional steam is produced for the turbine in the clinker
cooler 20 from cooling the hot clinker discharged from the kiln 16
via line 19.
Sulfur compounds in the fuel or in the cement raw materials are
mainly released in the CFB reactor 1 as SO.sub.2. In traditional
CFB steam production units, the amount of limestone needs to be
minimized--Ca/S molar ratio typically around 2--to minimize
operating costs. In the present method, Ca/S molar ratios greater
than 3 can be used in the CFB to improve the sulfur capture from
flue gas exiting the system via stack 41. No attendant increase in
operating costs results since a very high amount of calcium
relative to sulfur is inherent in the cement clinker making
process. A very high sulfur removal efficiency (greater than 98%)
in the flue gases in line 38 can also be achieved by re-injecting a
portion of the lime-rich solids 39 into the flue gas leading to the
filter 37 and by simultaneously controlling the relative humidity
in the flue gas by moisture addition or temperature control. This
might be necessary for high-sulfur fuels, where the portion of the
sulfur in the cement raw mix released in kiln 16 and carried back
to boiler flue gas 32 may be significant.
Regarding the Cement Production
A major feature of the invention is the integrated coproduction of
power and cement, in which coproduction the ashes of the power
production are used to replace part of the cement raw mix in the
cement production. Indeed coal ashes are similar in composition to
calcined clays. Moreover all of the coal residues are converted
into cement, the sulfur is absorbed by clinker component CaO.
As described above, two inlets 3 and 3a for the raw cement mix are
provided in the reactor 1. Via line 3, a part of limestone is fed
into the reactor in pulverized form; typically 90% of the limestone
particles are smaller than 90 microns, the size being appropriate
for the cement clinkering process. Via line 3a the remaining part
of crushed limestone is introduced to form bed and circulating
material. At temperatures above about 800.degree. C., limestone
CaCO.sub.3 is calcined into CaO. CaO combines with SO.sub.2
released from coal combustion and oxygen to form gypsum CaSO.sub.4.
SO.sub.2 can be disposed by standard wet or dry scrubbing methods
using limestone. Enhanced dry scrubbing methods are included such
as hydrating the calcined lime before introduction into the low
temperature SO.sub.2 -laden flue gas stream and/or recirculating
the calcium-rich solids from the filter back into the duct leading
to the filter 37 and/or cooling the flue gas stream leading to the
filter 37.
Draining off solids controls solids inventory in the combustor. The
hot solids drained of the fluidizing bed via line 11 are cooled
down through an ash cooler 43. They are introduced in a grinder 12
in which they are ground to an extent that 90% are below 90 .mu.m.
They are mixed with additives introduced in the grinder by a line
14 and with some of the cement raw mix (not shown). These
corrective additives are used, if any essential chemical compound
needed in the mixture of coal ash and limestone like iron oxide or
silica content are not present in the required amount.
The ground material is supplied to a blender 15, in which is added
the lime CaO via a supply 15. This amount of lime is constituted by
the solids separated in the filter 37 and is fed via line 39. To
achieve this amount of lime coming from filter 37, the cyclone 8 is
designed to separate the predominant char and crushed cement
material from the remaining components. Since the mean size of the
ash and the lime is typically smaller than 50 .mu.m it will escape
the cyclone, while the char and the crushed lime/limestone, which
is far greater in size will be retained in the cyclone. Thus the
fly ash escaping the cyclone consists predominantly of lime and is
forwarded with the flue gas in line 32.
In a preferred embodiment, the calcined raw mix may be preheated
after the blender 13 before Introduction into the kiln 16. This
allows decreasing the size of the kiln 16. The calcined raw mix of
the correct size and composition for cement clinker making is then
introduced into a riser tube 51 via line 17. To increase the cement
raw mix temperature, a small amount of fuel is fired in the riser
tube 51 along with preheated air coming from line 26 out of the
clinker cooler 20. The fuel is supplied via a line 52. At its exit
the tube connects the kiln exit and a cyclone 53. The cyclone 53
discharges the heated cement raw mix via line 54 into the kiln
16.
The gases leaving the cyclone 53 are mixed into line 32 with the
flue gases leaving the CFB cyclone 8. Since the kiln 16 is
typically operated under slightly negative pressure to avoid
leakage of hot gases into the environment and since the inlet air
for the CFB is required to be under positive pressure to overcome
the pressure drop in the bed and freeboard, the kiln exhaust cannot
be ducted to the CFB inlet. Instead, the kiln exhaust is added to
flue gases leaving the CFB cyclone 8, where the pressure levels are
compatible.
In the rotary kiln 16, the preheated and calcined raw mix is burnt
into cement clinker. For combustion in the kiln 16, a small amount
of fuel, i.e. coal is injected via a lance 18 together with the
preheated air in line 25. The cement clinker--in form of
nodules--is then forwarded via line 19 into a cement cooler 20,
which might be a moving grate. Besides air preheating, in the
present example is also shown steam production in the cement
cooler. This steam may be injected in an appropriate location in
the steam turbine island 42. The cooled clinker nodules are finally
supplied to a cement grinder, which is not shown.
When using high sulfur fuels, a portion of the sulfur captured by
the lime in the CFB reactor 1 would be released In the kiln 16 due
to the high processing temperatures. It might also be necessary to
control the sulfur content of the clinker to below a certain value
(typically 2.5 to 3% SO.sub.3) to obtain acceptable clinker
quality. An acceptable sulfur content in the clinker can be
achieved, for example, by controlling the level of oxidizing
conditions In the kiln, with the SO.sub.2 being released into the
flue gas leaving the kiln. The flue gas stream exiting the kiln 16,
relatively concentrated in SO.sub.2, can be cost-effectively
treated by taking a portion of it and cleaning it in a wet
limestone scrubber to a valuable product gypsum, which can be added
to the final cement product.
A bypass flue gas line 45 is connected to a flue gas cooler 46 and
a filter 47. This filter could be an electrostatic precipitator
wherein the entrained particles are separated, the coarse particles
being returned to the process and the fine particles being
separately disposed. A fan 48 and a limestone scrubber 49 follow
the electrostatic precipitator downstream. The gas exit of the
scrubber is connected to stack 11. Combining CaCO3 with SO.sub.2
and oxygen form gypsum CaSO4 in the limestone scrubber. This gypsum
can be used as an additive to ground clinker in the final cement
product.
The invention may be illustrated in more detail with reference to a
numerical example: It goes without saying that absolute values
cannot be specified in connection with the said numerical values
with regard to the dimensioning of the involved apparatus, since
absolute values are in any case not meaningful enough on account of
their dependence on numerous parameters.
For obtaining an electrical output of 220 MW and a cement output of
35 kg/sec, a total airflow of 233 kg/sec, coal in the amount of
23.3 kg/sec, limestone in the amount of 43 kg/sec and 8 kg/sec
additives are needed. A higher ash coal will typically require
fewer amounts of additives
220 kg/s of ambient air is sucked in by fan 27 to the air preheater
28 and is heated therein to 350.degree. C. 12 kg/s of ambient air
is sucked in by fan 22 into the clinker cooler. The air leaves the
cooler at around 1100.degree. C. The remainder of the cooling of
the clinker nodules down to around 100.degree. C. is accompanied
with steam production for the turbine. From the air leaving the
cooler, 3 kg/s are fed to the kiln via line 25 and 9 kg/s are
bypassing the kiln via line 24 into the riser tube 51. The gas
amount out of the kiln is about 4,4 kg/s at 1100.degree. C. The
total gas leaving the cyclone 53 is 14.3 kg/s and is combined with
the flue gas leaving the CFB cyclone 8. The fluidizing air fed to
the bed bottom via supply 5 is in the amount of 110 kg/s and the
overbed air via supply 4 is in the amount of 110 kg/s. The flue gas
in line 45 is in the amount of 1.0 kg/s at 1100.degree. C. The
temperature after the cooler 46 is 150.degree. C.
Coal in the amount of 22 kg/s is injected in the CFB reactor 1 and
in the amount of 0.4 kg/s is injected into the kiln 16. The latter
is transported with 1 kg/s of primary air. Another 0.9 kg/s is
injected in the riser tube 51. Pulverized limestone in the amount
of 39 kg/sec and crushed limestone in the amount of 4 kg/sec are
introduced in the reactor 1. In the fluidized bed reactor 2500-4600
kg/sec are typically circulated. The bed drain of the reactor is at
about 3 kg/sec, the additives introduced in grinder 12 are at about
8 kg/sec and the lime separated In filter 37 and fed to blender 13
is in the amount of 24 kg/sec. Thus 35 kg/sec of calcined raw mix
are supplied to the kiln.
The hot solids of the bed drain are cooled down in apparatus 42 to
around 200.degree. C. The gas and the solids exiting the reactor
and entering the cyclone 8 have a temperature between 800 and
1200.degree. C. An amount of 85% of the hot solids out of the
cyclone 8 is returned uncooled to the reactor 1, while 15% are
supplied to the fluidized bed heat exchanger 9 and cooled down
therein to ca. 400.degree. C. Of course this temperature depends on
the amount of heat extracted for steam superheating or
reheating.
Downstream the cyclone 8, the escaped gas is in the amount of 275
kg/sec and the escaped fly ash is in the amount of 24 kg/sec. In
the example shown, the gas and the fly ash are cooled down in the
steam heat exchanger 33 to 350.degree. C. and further in the air
cooler 28 to 100.degree. C.
It might be that about 0.5 kg/s carbon is contained in the fly ash.
This carbon is separated in the filter 37 with the lime and fed to
the kiln. In this case either the coal amount to the kiln has to be
reduced appropriately or the amount of air through the kiln has to
be augmented to bum the supplemental 0.5 kg/sec carbon.
Of course, the invention is not restricted to the plant shown and
described. The invention can be used irrespective of the type and
design of the combustor. This combustor could as well be an
apparatus with entrained flow, if a pulverized fuel is used.
Instead of cyclones, separating apparatus with moving bed could be
used as well. A larger air cooler could replace the steam heat
exchanger 33 and the air cooler 28. This would preheat the air in
line 29/30 to about 750.degree. C. and provide a high temperature
driving force for steam generation in apparatus 35 and 36. It is
understood that--depending on the amount of heat being available
and being extracted--preheating, evaporating, superheating and
reheating may occur in all apparatus 34, 35 and 36 and in the
clinker cooler 20.
Obviously, numerous modifications and variations of the present
invention are possible in light of the above teachings. It is
therefore to be understood that, within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described herein.
List of Designations 1 circulating fluidized bed 2 hydrocarbon feed
line 3, 3a limestone feed line 4 secondary (overbed) air line to 1
5 fluidizing air supply 6 solids return line 7 solids return line
bypassing 9 8 cyclone 9 fluidized bed heat exchanger 10 solids
return line to 9 11 hot bed material discharge 12 grinder 13
blender 14 additive supply to 12 15 lime supply to 13 16 kiln 17
calcined material line to 51 18 fuel supply to 16, coal 19 kiln
clinker discharge line, nodules 20 clinker cooler 21 line to
clinker grinder 22 fan 23 air supply to 20 25 air supply to 16 26
air line bypassing kiln 16 27 fan 28 air heater 29 air supply to
air heater 30 hot air discharge from air heater, air supply to 1 32
gas and fly ash line 33 steam heat exchanger 34 economizer 35
evaporator 36 superheater and reheater 37 filter, electrostatic
precipitator 38 gas exhaust line 39 lime discharge line from 37 40
fan 41 stack 42 steam turbine island 43 hot solids cooler 44 second
air discharge from 20 45 bypass flue gas from kiln 16 46 flue gas
cooler 47 filter 48 fan 49 limestone scrubber 51 riser tube 52 coal
supply to 51 53 cyclone of 51 54 calcined material line to 16
* * * * *